The primary objective of this research is to advance and refine our basic understanding of how afferent and centrally-patterned neural inputs affect the discharge of lip muscle motoneurons involved in human speech production. A related goal is to test for perioral reflex excitability differences in stutterers and nonstutterers. These problems will be studied by stimulating the perioral and auditory receptor systems prior to and during lip muscle contraction for various speech and nonspeech gestures. Observations on the voluntary and reflexive electromyographic responses of the perioral muscles will then be used to infer the characteristics of the underlying neural control processes involved in human speech production. This should enhance our understanding of certain speech production disorders, the neural encoding of linguistic units, the use of perioral reflex testing in studying cranial motor physiology, and the function of mechanoreceptor feedback in the neural control of human muscle contraction.